Transmission of pictures by electricity



Sept. 11, 1928.

H. E. IVES TRANSMISSION OF PICTURES BY ELECTRICITY Filed March 1925 Patented Sept. 11, 1928.

TES

UNITED STA mm'nnn'r E. IVES, or MONTGLAIR, NEW JERSEY, Assreivon, BY mnsns ASSIGNMENTS, 'rol gilfwflmncmmc COMPANY, moonrona'rnn, A CORPORATION on NEW YORK.

. "Application filed March '2, 1925. Serial m). 12,694.

Thisinvention relates to signal receiving and recording apparatus and more particularly to receiving apparatus for picture transmission systems.

In the transmission of pictures by electrical means it is usual to transmit to the receivin station a series of signals or impulses w ich are in some way characteristic of elementary portions of the picture or subject being transmitted. At the receiving station these signals are employed in various ways for forming a reproduction of the original. According to one method of reproducing pictures a llght valve is operated by the received signals to vary the exposure of elementary portions of a light sensitive film forming light and dark areas similar to the elementary areas of the original subject. It is customary to mount the light sensitive film upon a rotating drum, so that the entire area is exposed in a succession of helical traces. In one form of light valve used for this purpose, a shutter for a light aperture consists of a movable-string or ribbon in a magnetic field. Variations of the signaling impulses passing through the string cause it to move in the direction of the trace on the recording film to expose a portion of the light aperture of the valve corresponding to the signal. In applicants Patent No. 1,667,- 805, May 1, 1928, a light valve is described which operates on alternating current moving the string perpendicularly with respect to the direction of the trace to produce successive lines of varying width which make up a picture. 'The present invention combines certain features of these systems to produce a simplified and improved system of reproducing pictures which are faithful reproductions of the original.

' -.One ofthe-objects of the present invention is to improve the method and means employed .for-I reproducing-pictures in picture transmission systems;

'Another object 'offthe invention is to improve the method of recording the signals 1 employed in the 'transmissionof pictures by electricalmeans.

Still another object is to improve the faithfulness of reproduction in picture transmission systems employing modulated carrier waves.

In one arrangement of apparatus for at taining these objects a light valve is employed in which a single string'shutter element wide enough to cover a light aperture 1s positioned so as to vibrate in the direction of movement of a rotating recording drum. Picture modulated carrier current; is impressed on the light valve causing the string to vibrate with an amplitude dependent upon the signaling Waves to expose the light aperture first on one side of the string and then on the other. In this way successive exposures of varying density are formed on the recording film producing true half tone pictures.

Other objects and advantages of the invention will become apparent from the following description and drawing in which:

Fig. 1 is a perspective view of a portion of the light valve showing the relation of the string to the light aperture.

Fig. 2 is a diagrammatic view of the light valve and recording cylinder.

Fig. 3 is a diagrammatic view of the optical system taken at right angles relatively to the view shown in Fig. 2.

Fig. 4 illustrates the form of a typical modulated carrier wave.

Fig. 5 is a diagram showing the movement of the string of the light valve.

Fig. 6 is the trace on the recording film corresponding to the movement of the string of the light valve shown in Fig. 5.

Fig. 7 illustrates a cross section greatly enlarged of a photographic film as exposed in reproducing the picture.

Fig. 8 is a side view of the portion of the light valve shown in Fig. 1.

In the present invention applicant employs a light valve consisting of a field magnet 12 having a slit aperture 13 through which light from the source 14 passes. The width of the slit should be negligible as compared with the length, good results being obtained with a light aperture .035" long and .008 or .009 wide.

The effective width of the light a erture may be varied by means of adjustable jaws 20, one of Which, is broken away as shown in Fig. 1 to show the relation of the various parts. This eriablessubstitute shutter elements which may differslightly in width to position of the pivoted member 21, by rotation of the screw 22 for accurately adjustin the length of the aperture.

Fositioned directly in front of the aper- 6 ture 13 is a movable shutter element in the form of a string or ribbon 15 slightly wider than the aperture itself. Carrier current modulated in accordance with signals is impressed on the shutter element by means of the transformer 24:. Since the string is located in the field of magnet 12, carrier current passing through it causes it to be displaced to a degree varying with the amplitude of the carrier wave impressed on the transformer 24 in the light valve circuit. The shutter element will, therefore, vibrate back and forth in front of the light aperture. Light from source 14 focused on the light valve aperture by lens 16 passes the 20 light valve shutter first on one side of the string and then on the other. A light valve of this character is described in further detail in applicants patent referred to above. In the present invention, a recording light sensitive film 18, is mounted on a rotating drum 19 which is moved axially by means of a supporting member having threads of a very small pitch. The drum and light valve are so mounted that the string of the light valve vibrates in the direction of motion of the moving recording film. In this way the surface of the film is passed over in a series of helical traces side by side. The length of the light aperture of the light valve is adjusted by means of screw 22 so that successive traces on the film are exactly adjacent to one another.

In reproducing a picture, carrier current modulated in accordance with the picture is 40 transmitted to the receiving station and impressed on the light valve circuit. Such a modulated carrier wave is illustrated in Fig. 4 of the drawings. In Fig. 5 the movement of the light valve shutter is plotted against time, assuming the current in .the light valve circuit to be that represented by the curve of Fig. 4. The width of'the light valve aperture is indicated as (Z- and for the purpose of simplicity, the shutter of the light valve is shown just the same width as the aperture. Vhen the string moves upwardly during the first half cycle of the carrier (1, the light aperture is exposed as shown by the cross hatched area a. This causes an ex- 'posure of the recording film corresponding to a". .zero the string moves back in front of the light aperture but immediately exposes the aperture on the opposite side of the string as indicated by the cross hatched area 6 forming an exposure on the recording film corresponding to Z). Thus, as the signals are received there is an exposure on the recording element for each half cycle of the carrier corresponding to the amplitude of the wave and therefore corresponding to the light characteristics of the original subject at the sending station.

In applicants patent referred to abovethere is described a light valve operating in a somewhat similar manner with the string of the light valve vibrating in a direction perpendicular to the direction of movement of the recording element to form lines of varyin width on the recording element corresponding to the light characteristics of the subject." In the present invention the string of the light valve vibrates parallel to the direction of movement of the recording element so that the two exposures-on the recording element are of the same width and in succession following the traces instead of side by side as in the form of light valve referred to above. This is clearly shownin Fig. 6 which illustrates a singletrace on a photosensitive film as exposed by the movement of the string of the light valve. The trace is greatly enlarged to more clearly show the characteristics of the exposure.

The exposure of the light aperture as indicated by cross hatched portion a of Fig. 5

gives as a light source for producing a chemical change in the recording film, -a very narrow band of light of slight intensity.

The chemical change produced on the film or record or any other recording element is correspondingly small and the density of the trace is not very great as shown at a" in Fig. 6. As the string moves to expose the aperture atb, another exposure of characteristic density is formed as at Z in Fig. 6 and so on along the trace. Each successive trace is the same width so that the resultant picture is not one of separate and distinct lines but a true-half tone product-ion similar to the original.

Fig. 7 may be considered as indicating a graph of the light intensity plotted against time but it is better considered as a magnified cross section of the recording film when de veloped. In this case the amount of light sensitive material converted into an insoluble compound is proportional to the light intensity. The portion of each cycle during which the light aperture is completely covered is exceedingly small sothat pictures produced by this method appear to the naked eye to be the same as the original. The detail of the subject is reproduced with the greatestaccuracy as is shown by the following ex- AS the current I'QWISQS and bBCOIntS- ample. If a carrier current of 1300 cycles is employed, the recording element is exposed 2600 times per second. A recording film moving at the rate of 10 per second will still have 260 exposures per inch along the trace. A 5 x 7 picture mounted on a recording drum 2" in diameter can be produced in less than 4% minutes with 60 successive lines or traces per inch. The character of the exposure is such that the line character of the reproduction is completely lost except as examined under the microscope. The speed of picture transmission may be increased to the limit of the mechanical elements of the combination.

The invention is not limited to the production of pictures. but may be utilized in recording any type of signal desired. While the invention has been disclosed in connec tion with the photographic recording of signals, it is obvious that otherlight sensitive elements may be actuated by the lightvariations to record the signals in any desired manner.

What is claimed is: 1. In a picture transmission system, a light source, a recording element, a source of alternating current, a light valve for controlling the light from said source falling upon said recording element, said light valve comprising asingle string shutter element, and means for applying said alternating current to said valve to vibrate said string in the direction of movement of said recording element.

2. The combination with a moving recording element, of a light valve operated by alternating current, said valve comprising a single string shutter element vibrating in the direction of motion of said recording element.

3. Thecombination with a moving recording element, of a source of alternating current, a light valve comprising a light aperture and a single string shutter element, and means forv applying said current to said valve to vibrate said string in the direction of motion of said recording element to expose said light aperture on element.

4. The combination of a source of modulated alternating signal current, a moving reeither side of the shutter ing said current to said valve to vibrate said string 1n accordance with the modulations of said alternating current, said string moving in the direction of motion of said recording element to expose the light aperture twice with each cycle of the signaling current.

5. The method of reproducing a picture which comprises producing an alternating current carrier wave modulated according to the characteristics of the picture, and exposing a light sensitive surface in successive elemental areas of uniform width, the degree ofexposure of each area being determinedby the amplitude of a corresponding half cycle of said carrier wave.

6. In a system for producing images by electrical transmission, a light source, a light receiving element, a source of alternating current, a light valve for controlling the light from said source falling upon said light receiving element, said light valve comprising a single string shutter element, means to produce relative movement between said light receiving element and the light rays from said light source, and means for applying said alternating current to said valve to vibrate said string in the direction of relative movement between said light receiving element and said light rays.

7. The combination with a moving light receiving element, of a light valve operated by alternating current, said valve comprising a single string shutter element vibrating in the direction of motion of said light receiving element.

In witness whereof, I hereunto subscribe my name this 2 day of March, A. D. 1925.

HERBERT-E. IVES. 

